Markdown is supposed to be readable without rich text formatting.

There's no one way of displaying markdown as long as the semantic structure is respected. Dashes, hyphens, circles or dots. Don't matter as long as it's an unordered bulleted list and the correct hierarchy and sequence is followed for each block of text. Similarly the indentation of all those things is irrelevant and to the taste of the reader's implementation.

You don't indent text in markdown to signal formatting. You indent text in markdown to signal a code block. To signal other semantic structures you use other plaintext markers.

Read the original definition of the format to understand which are they. The purpose of markdown is to write the same general and commonly used mark-up elements used in HTML (paragraph, links, references, lists, tables and emphasis, amongst many others) with plaintext, in a less verbose and more human friendly way. And just like HTML, the formatting is supposed to be separate. With CSS or such other techniques. As a result, the formatting is free to change while the underlying structure and meaning of text stays the same.

I would guess it is how each developer choose to implement it. Markdown is really just simple text. Usually apps are enriching it based on that, but each can implement it differently. Obsidian.md is how I like my Markdown to look. But it’s not a Lemmy app. I think they use front-matter or something